An image pickup lens unit included in mobile phones has a structure in which a surrounding of an optical lens is held by a holder. Typically, the optical lens is mounted into the holder by an automatic assembly system that has a very high positioning accuracy and uses an image recognition technique. However, such a system is not only very costly, but also requires a very large space because production lines are set up for different steps, such as a step of inserting a lens into a holder and a step of bonding the lens to the holder. As a result, facility replacement carried out for each change of lens type involves very extensive work, and hence many worker-hours are required.
A manufacturing method that addresses the problems described above is known. In this method, first, a plurality of resin optical lenses and a holder body and a cover for holding the optical lenses are individually molded in different portions of the same mold. Next, these resin members are moved and assembled while the holder body remains in the mold. Then, molding is performed again to form a molded assembly (see Patent Literature (PTL) 1).
Another manufacturing method is known in which, after an optical glass lens and a stop (or diaphragm) are positioned and set in a mold in advance, a holder is formed around the optical glass lens by injection molding to assemble an image pickup lens unit at the same time (see PTL 2).
However, the manufacturing method disclosed in PTL 1 is disadvantageous in that it increases the number of molded components for joining the cover to the holder body and makes the molding step complicated. Additionally, since a resin flow path for such joining components needs to be created, it is very difficult to ensure filling properties and joint strength of a thin-wall holder used in an image pickup lens unit to be included in mobile phones. Therefore, it is difficult to achieve downsizing desired for such an image pickup lens unit to be included in mobile phones.
Also, in the manufacturing method disclosed in PTL 2, the optical lens and the stop need to be directly held between molds. If the holding force is not sufficient enough, resin that flows out through gaps may adhere to the optical surface of the optical lens or to the stop. On the other hand, if the holding force is too large, the optical lens or the stop may be deformed or damaged. Thus, since the allowable range of holding force is narrow, it is very difficult to carry out the holding operation. Additionally, since a positioning shape for positioning the lens is formed in the molds, the positioning shape may remain as a visible depression in the resulting molded part. Then, the entry of unnecessary light into the depression may cause optical defects, such as ghosts and flares. At the same time, visual specifications required for the image pickup lens unit to be included in products, such as image pickup apparatuses, may not be met. Moreover, such a positioning shape may cause deformation during mold releasing and may deteriorate the dimensional accuracy.